1. Field of the Invention
The present invention provides an optical structure, in particular, to a light guide module for use in a projection apparatus and the projection apparatus.
2. Descriptions of the Related Art
DLP (Digital Light Processing) projectors, which are developed by Texas Instruments, are projection displays that utilize a particular light source modulation scheme. The most prominent feature of DLP projectors is that, as a fully digitalized reflection projector, they can not only present finer projection images, but also allow for effective reduction in both volume and weight of the projectors, thereby making the projectors lighter, thinner, shorter and smaller. DLP projectors are classified into either single-chip or three-chip projectors, and are mainly used as super-lightweight portable and high-luminance projectors.
A DLP projector comprises a light source, a color wheel, a digital micromirror device (DMD) chip and a projection lens. Light from the light source is collected by a light collecting cover, focused via a lens and then sent through filters of three colors (i.e., red, green and blue) on a color wheel to the DMD chip. A memory associate with each pixel of the DMD records the value of a digital signal corresponding to the pixel, while the digital signal is transmitted to a drive electrode to induce positive or negative deflections of the micromirrors and control the deflection time. By controlling the rotational speed of the color wheel, alternation of the three primary colors (i.e., red, green and blue) can be accomplished to obtain a full color effect.
FIG. 1 is a schematic view of a projection apparatus 1 that adopts the conventional DLP technology. The projection apparatus 1 comprises a light source 101, a color wheel 103, a light integration rod 105, a relay mirror assembly 107, a TIR (Total Internal Reflection) prism 109 (including a first prism 109a and a second prism 109b), a DMD 111 and a projection lens 113. It should be noted that the color wheel 103 has three primary colors formed on individual portions adjacent to each other, with each color being formed on one portion respectively. Between a surface 1091 of the first prism 109a and a surface 1092 of the second prism 109b, there is an air gap 110. The two surfaces 1091, 1092 are substantially parallel to each other.
The light source 101 emits a white light beam (as indicated by the arrow), which is adapted to pass through the rotatable color wheel 103 to be split into different color lights. Then, the color lights travel through the light integration rod 105 to the relay mirror assembly 107. It should be particularly noted that the relay mirror assembly 107 comprises a first reflecting mirror 107a and a second reflecting mirror 107b, while the color lights exiting from the light integration rod 105 are reflected sequentially by the first reflecting mirror 107a and the second reflecting mirror 107b to the first prism 109a. The first reflecting mirror 107a and the second reflecting mirror 107b are not in the same plane, so there is a three-dimensional rotation of the light beam reflected by these surfaces.
Upon entering the first prism 109a, the color lights undergo a total internal reflection and then travel to the DMD 111. Then, the color lights are selectively reflected by the DMD 111 back to the first prism 109a, passes through the first prism 109a, the air gap 110 and the second prism 109b in turn, and finally enters the projection lens 113 to form an image to be projected.
However, the design of the projection apparatus 1 has the following disadvantages:
Firstly, in the conventional projection apparatus, the light integration rod 105 has a profile (e.g., a rectangle with an aspect ratio of 16:9, with a long direction thereof lying in the vertical direction) that is rotated by 90° relative to that of the DMD 111 (e.g., a rectangle with an aspect ratio of 9:16, with a long direction thereof lying in the horizontal direction). In more detail, after passing through the light integration rod 105, the light beam will also present a rectangular profile whose long direction lies in the vertical direction and whose aspect ratio is 16:9. When this incident light beam is guided by the rotation of the first reflecting mirror 107a, the reflected light beam thereof will exhibit a profile whose normal direction is rotated by a certain angle relative to the incident direction and then enters the second reflecting mirror 107b. Afterwards, the light beam is guided by the rotation of the second reflecting mirror 107b again, causing the normal direction of the reflected light beam's profile to be rotated by a further angle before the light beam enters the TIR prism 109. As a result, the light beam entering the TIR prism 109 has a rectangular profile whose long direction lies in the horizontal direction with an aspect ratio of 9:16. Then, through a TIR in the TIR prism 109, the light beam is reflected to the DMD 111 to be imaged and then is projected the projection lens 113. As the reflected light beam presents attenuated luminance, this may degrade the utilization efficiency of the light source within the projection apparatus to an extent that the image finally obtained has inadequate luminance.
Secondly, to collect light effectively in the aforesaid projection apparatus between the light integration rod and multiple light sources, the optical structure is designed in such a way that two light sources, namely a left and a right light sources, are arranged at an upper and a lower position respectively (i.e., arranged asymmetrically with one at an upper left position and the other at a lower right position; or alternatively, with one at a lower left position and the other at an upper right position). Three light integration rods are used (i.e., two of them are arranged at an upper and a lower position respectively near the light sources, and the third one is arranged far away from the light sources to integrate light beams from the aforesaid two light integration rods). Consequently, the conventional projection apparatus with multiple light sources is difficult to design and exhibits a poor space utilization.
Thirdly, in the projection apparatus 1, a fixing structure (not shown) is needed to position the reflecting mirrors 107a, 107b. However, because orientations of the mirrors have a direct influence on the light path, they must be positioned accurately in order to ensure a correct light path. Consequently, the procedure of positioning the mirror assembly is very complex and tedious, which is unfavorable for mass production of projection apparatuses.
In view of this, it is important to provide a projection apparatus with improved imaging quality, miniaturized profile and light weight by improving the complex light path design of the conventional projection apparatus and reducing loss of luminance of the light source.